Knife sharpening device



Jan. 7, 1964 c. L. CLARK 1 KNIFE SHARPENING DEVICE Filed Feb. 7, 1965 United States Patent 3,116,577 KNIFE SHARPENIN G DEVICE Carl L. Clark, 376 Central Pkwy. SE., Warren, Ohio Filed Feb. 7, 1963, Ser. No. 257 ,813 3 Claims. (Cl. 51-218) This invention relates to a device adapted for holding the blades of knives such as kitchen and butcher knives for sharpening. It is designed for use with a sharpening stone with flat parallel surfaces.

More specifically, the present invention comprises a device for holding a knife blade at a predetermined angle in relation to the fiat sharpening surface of an oil stone, for sharpening such knives as kitchen and butcher knives having a cutting edge comprising a substantially straight portion and a more or less long convex tapered portion terminating in a point.

Since the durability of a cutting edge of a knife, aside from the quality and temper of the steel, depends on the proper sharpening angle, this device will hold the blade at the correct angle with reference to the sharpening surface of the stone. This angle is generally accepted to be about twenty degrees.

In the drawings:

FIG. 1 is a side elevation of the sharpening device and shows the relative positions of the knife blade, oil stone and knife holding device during the sharpening operation.

FIG. 2 is an end elevation of that portion of the knife holding device that rests on the flat surface which forms a common support for this portion of the device and the oil stone.

FIG. 3 is a plan view showing, the oil stone, and the sharpening device with the knife blade clamped in same. It also shows the curved ends of that portion of the knife holding device that rests on the flat surface which supports both the oil stone and the device.

FIG. 4 is an end elevation of the device showing the required tilting angle so that the extreme point of the knife blade can be sharpened.

Referring to the drawings FIGS. 1 and 2, the device comp-rises a bar 6 one end of which is shaped to hold the knife blade at twenty degrees to the sharpening surface of the stone by means of a clamping device mounted on bar 6, comprising a clamp 5 and a clamping spring 7. At the other end of said bar is a support member 8 adapted to remain in contact with the flat surface on which the sharpening stone is mounted during the sharpening opeartion. Bar 6 is usually made so that the distance from the knife blade cutting edge to the support member 8 is in the neighborhood of four inches more or less.

To operate the device, the knife blade 4 is clamped as shown in FIG. 3, placed in a horizontal position on the sharpening stone and is moved about by the operator in a rotary motion to sharpen the straight portion of the cutting edge.

To sharpen the convex portion of the cutting edge of the blade, the operator slowly raises the end of the handle until the point of the blade engages the surface of the sharpening stone as shown in FIG. 4. During this raising of the handle end the rotary sharpening motion is continued. The above described operation is the procedure to sharpen one side of the knife blade. To sharpen the opposite side, the knife is removed from the device, reversed end for end and reclamped therein. The operator then repeats the above operation to sharpen the opposite side.

To maintain the correct sharpening angle while sharpening the tapered convex end portion of the knife blade, the lower edge of support member 8 is contoured to a convex shape. This provides a correction to main the cutting angle at or close to twenty degrees. An additional correcting means is provided to more nearly hold the cutting edge at said angle when sharpening this tapered end portion of the knife blade. This means consists of the outwardly curved ends of support member 8 as shown in FIG. 3.

In FIG. 3 the knife is indicated by 9. Projecting the position of 9 in FIG. 3 to FIG. 1 it will take the position of d shown in PEG. 1 'when sharpening the straight portion of the blade. Imagine now that point 9 drops to contact the sharpening surface 3, it will take position It in FIG. 1. it is therefore evident that distance A in FIG. 1 is the amount of shortening of the distance of blade point 9 to the support member 8 in comparison with the distance of the cutting edge of the straight portion of the knife blade to said support member. Therefore in sharpening the tapered portion of the blade, the sharpening angle would change from that for sharpening the straight portion of the cutting edge unless a correction in the angle is made. To make this correction, the ends of support member 8, as shown in FIG. 3, are bent outward this distance A. These bent portions of 8, in combination with the convex surface of the support member 8, maintain the sharpening angle closely to the twenty degrees held for sharpening the straight cutting edge of the knife blade. These two elements of the design, namely the convex surface and outwardly bent ends of the support member 8, are important useful and novel features of this knife blade sharpening device.

The shape of the convex surface of support member 8, which remains contact with the flat surface 2 during the sharpening operation, as shown in H68. 2 and 4, was chosen after careful experimentation. With this convex surface, curved as shown, I have proved by actual tests, with the aid of a sensitive machinists level that the blade of the knife when sharpening the convex tapered portion of the cutting edge will not vary in angularity to the fiat surface 3 of the sharpening stone by more than one degree from the sharpening angle when sharpening the straight portion of the cutting edge. This I found to be tnue even for longer knives with much longer convex tape-red cutting edges than that of the short knife shown in my drawing. In other words, the sharpening device of the design shown, will equally well sharpen both short and long knife blades and closely maintain the desired sharpening angle.

1 have also tested with the level noted in the preceding paragraph, a sharpening device similar to that shown in my drawing, but with the exception that the convex surface of support member 8, as shown in FIGURES 2 and 4 is replaced by a straight surface positioned tangent to the center of said convex surface and lengthwise thereto. It is also straight instead of curved at the ends as support member 8 is shown in FIG. 3. In these tests I found that, as the device was tilted to sharpen the convex tapered portion of the cutting edge, the inclination of the blade to the sharpening surface changed as much as 6 to 7 derees from the selected sharpening angle. This means a change in the included angle of the cutting edge of 12 to 14 degrees. Therefor, the convex surface of support member 8, which is curved both upward and outward, makes it possible to sharpen both long and short blades with equal precision. To obtain this precision in sharpening the curved tapered portion of the blade cutting edge, the device is purposly clamped so that the point of the blade, as shown in plan view, FIG. 3 of the drawing, extends beyond the clamping means of the device to a point approximately in line with the forwardly extending tip end of support member 3.

The clamping means shown in the drawing is subordinate to the two basic elements of the design, namely, the convexly curved surface of support member 8, and the outwardly curved ends of said support member. Other 3 simple mechanical means for clamping or holding the knife blade in the device are equally adaptable. This clamping means shown is simply to convey the necessity of holding the knife blade in the device securely and at the proper sharpening angle. its function is to hold the knife blade in the device at the correct sharpening angle and prevent slippage or angular movement of the blade in relation to support member 8.

Having thus described my invention, what I claim as new, and desire to secure by United States Letters Patent is:

1. In a device to be used in combination with a fiat surfaced sharpening stone for sharpening the cutting edge of the blades of kitchen knives and the like, when the blade is placed in contact with said stone and moved over same, said blades having cutting edges with both straight and convex tapered portions, and said device being designed to maintain said knife blade in a selected angular relationship with the sharpening surface of said stone, said device comprising a bar having at one end means for holding said blade in a selected angular relationship thereto, and at the other end a support member for supporting said bar and arranged to contact said flat surface, said support member comprising a central portion extending in a substantially parallel direction lengthwise to said blade when said blade is held in place on said bar, and end portions of said member being curved upwardly and also curved outwardly from the cutting blade for contacting said flat surface as the device is tilted for sharpening the convex tapered portion of said blade.

2. In a device designed to be used in combination with a sharpening stone for sharpening the cutting edge of the blades of kitchen knives and the like, the blades of said knives having cutting edges with both straight and convex tapered portions, said sharpening stone being supported on a flat surface so positioned that the sharpening surface is substantially parallel thereto, and said device being designed to maintain the cutting edge of said blades in contact with the sharpening surface of said stone and in a selected angular relationship thereto, said device comprising a bar having at one end means for holding said blade in a selected angular relationship thereto during the sharpening operation, and at the other end a support member, said member having a convex surface contacting said flat surface, and also having outwardly curved ends which come in contact with said fiat surface as the device is tilted for sharpening the convex tapered portion of the cutting edge of said knife blade.

3. In a device designed to hold and maintain the blades of kitchen knives and the like in a selected angular relationship to the sharpening surface of a stone, as said knives are moved over and in contact with said stone during the sharpening operation, whereby the straight portion and also the convexly curved portion of the knife blade cutting edge is sharpened to substantially the same included cutting edge angle as measured in a plane normat to the straight cutting edge and also in a plane normal to the tangent to any given point on the curved portion of the cutting edge of said blade, said device comprising, a bar extending in a direction substantially normal to said blade and having at one end means for bolding the blade of said knife in a selected angular relationship thereto, and at its other end a bar support member being arranged tocontact said stone supporting surface durin the sharpening operation, said bar support member extending on both sides of said bar and the outer ends of said bar support member being convexly curved outwardly and away from said blade, and the bottom surface of said bar support member where it contacts said stone supporting surface being convexly curved upwardly on each side of said bar, and said bottom surface of said support member, at a convexly curved end thereof, comes in contact with said stone supporting surface as the device is tilted to sharpen the curved portion of the cutting edge of said blade.

References Cited in the file of this patent UNITED STATES PATENTS 2,741,077 Ayer Apr. 10, 1956 2,864,206 Lane et a1. Dec. 16, 1958 FOREIGN PATENTS 905,102 Germany Feb. 25, 1954 217,934 Australia Oct. 13, 1958 

1. IN A DEVICE TO BE USED IN COMBINATION WITH A FLAT SURFACED SHARPENING STONE FOR SHARPENING THE CUTTING EDGE OF THE BLADES OF KITCHEN KNIVES AND THE LIKE, WHEN THE BLADE IS PLACED IN CONTACT WITH SAID STONE AND MOVED OVER SAME, SAID BLADES HAVING CUTTING EDGES WITH BOTH STRAIGHT AND CONVEX TAPERED PORTIONS, AND SAID DEVICE BEING DESIGNED TO MAINTAIN SAID KNIFE BLADE IN A SELECTED ANGULAR RELATIONSHIP WITH THE SHARPENING SURFACE OF SAID STONE, SAID DEVICE COMPRISING A BAR HAVING AT ONE END MEANS FOR HOLDING SAID BLADE IN A SELECTED ANGULAR RELATIONSHIP THERETO, AND AT THE OTHER END A SUPPORT MEMBER FOR SUPPORTING SAID BAR AND ARRANGED TO CONTACT SAID FLAT SURFACE, SAID SUPPORT MEMBER COMPRISING A CENTRAL PORTION EXTENDING IN A SUBSTANTIALLY PARALLEL DIRECTION LENGTHWISE TO SAID BLADE WHEN SAID BLADE IS HELD IN PLACE ON SAID BAR, AND END PORTIONS OF SAID MEMBER BEING CURVED UPWARDLY AND ALSO CURVED OUTWARDLY FROM THE CUTTING BLADE FOR CONTACTING SAID FLAT SURFACE AS THE DEVICE IS TILTED FOR SHARPENING THE CONVEX TAPERED PORTION OF SAID BLADE. 